Method of producing high-tensile strength deep-drawing steel



NOV. 20, 1945. w K E JR 2,389,516

METHOD OF PRODUCING HIGH-TENSILE S TRENGTH DEEP-DRAWING STEEL Filed. Nov. '24, 1941 FIG. 1. FIG. 2

INVENTOR: Jaws If A//v/v4, J6,

I ATTORNEY.

' Patented Nov. 20, 1945 METHOD F PRODUCING HIGH-TENSILE STRENGTH DEEP-DRAW'INQ STEEL James Kinnear, Jr., Pittsburgh, Pa. Application November 24, 1941, Serial No. 420,323

1 Claim.

This invention relates to the production of steel ingots, the primary objectbeing to produce ingots providing the desirable qualities of both deep-drawing rimmed steels and high-tensile strength killed steels.

' In explanation of the above, rimmed steel is a low-carbon oxidized steel which is permitted to effervesce for a period of time after it is cast into an ingot mold, the eifervescing serving to stir the metal during its solidification so as to produce a surface portion or skin of very clean low-carbon steel, the core or central portion of the ingot being subject to blow-holes and metalloid segregations.

The above steel possesses certain desirable qualities in that it can be rolled into products having a very fine surface finish and which are particularly adapted to forming operations involving extreme deformations of the metal. At the same time, the steel is neither very strong nor stiff, it being impossible to increase its carbon content to obtain greater strength and stiffness since it then could not be produced in the oxidized state required to produce the necessary effervescing action. For the same reason, none of the other common alloying elements which combines with oxygen to any great extent can be used as strengthening or stifiening alloys in rimmed steel.

Contrary to rimming steel, killed or deoxidized steel can be cast into an ingot mold containing any carbon content desired and containing alloying elements such as silicon and chromium which combine with oxygen. It is therefore possible to produce killed or deoxidized steel that is much stronger and stiller than rimmed steel. At the same time, however, killed steel lacks the fine surface finish and deep-forming qualities of rimmed steel.

According to the present invention the advantages of both rimmed and killed steels are combined in a single product by casting rimming or efiervescing steel into an ingot'mold to a height not exceeding that permitting a proper efier- 'vescing to proceed and allowing this steel to efiervesce or rim until the desired ingot skin is obtained.

7 At this point conventional procedure is to either cap the steel or place a plate on its top, although sometimes the steel is simply allowed to stand until it solidifies sumciently for stripping.. As previously explained, the resulting steel could be rolled into products having a fine finish and good deep-forming characteristics but which would be lacking in strength and stiffness.

additional metal is cast into the mold on top of the rimming or eifervescing steel. 'This metal may be plain-carbon steel, high-tensile strength alloy steel, or molten alloys or molten cast iron and shouldrbe, preferably, killed or deoxidized steel. In other words, this additional molten metal may be any high-tensile strength steel such as is normally cast to produce 9. killed or deoxidized steel ingot.

This additional molten metal is cast into the mold as soon as possible after the intially cast steel has rimmed to the extent desired and while 1 the core or central portion of this initially cast steel is still molten, The additional metal, for example a high-tensile strength steel, may be cast while the rimming or efl'ervescing steel initially cast is still in an active state.

As the first part of the additional steel is cast into the initially cast steel, it will mix with the liquid core or central portion of the rimming steel and may'not completely stop the efiervescing action if this is continuing, but as more is added it will displace this core or central portion so as to produce an ingot having the characteristic of a rimmed steel ingot insofar as its surface is concerned, but with its normal central portion replaced by the high-tensile strength steel which, as it solidifies, becomes integral with the normal skin of the rimmed steel ingot and with this skin substantially undisturbed in character.

The result of this practice is a steel product having a very clean surface of low-carbon content and a core of high-tensile strength steel. Furthermore, this core will be solid and free from material metalloid segregation since it comprises a killed or deoxidized steel. When rolled into products such as sheets the steel will have the strength and stiffness of high-tensile strength steel, such as a steel of relatively high-carbon content or one containing one or more of the strengthening alloys such as silicon and chromium or, for that matter, any of the recognized strengthening alloying elements. At the same time, the steel will have the finish and deepdrawing qualities of the relatively weaker and less elastic rimmed or effervescent steel.

High-tensile strength deep-drawing steel hasbeen produced in accordance with the present invention in the following manner:

Rimming or efiervescing steel analyzing at the ladle as containing .08% carbon, .38% manganese, )1 4% phosphorus and 935% sulphur was However, in the case ofthe present invention I poured to a height of 55 inches in a 31 inch by 31 inch mold and allowed to rim or efl'ervesce for 15 minutes. The weight of this ingot section was 12,700 pounds and at the end of the 15 minute period, 6700 pounds or killed or deoxidized steel was poured on topof this initially cast steel, this additional steel analyzing at the ladle as containing .78% carbon, .80% manganese, .02% phosphorus, .036% sulphur and .26% silicon.

The first or the additional or high carbon steel that was added to the ingot mold was diflused through the central portion or core 01' the rimming steel by the eflervescing oi the latter. However, as more of the additional steel was added, the strength of the rimming action decreased and eventually stopped by the time all of the additional steel was poured. Long rods were then used to stir the ingot, this giving an ingot with a clean low-carbon skin and a highcarbon central portion or core. 1

The total height of the final ingot was 85 inches and this ingot was heated and rolled into Y a slab, the portion of the slab forming the parts of the ingot and which did not have the desired low-carbon skin being cropped and discarded. The remainder of the slab was used to produce hot rolled flat material .102 inch thick which was then cold roller to .045 inch thick after which it was annealed for 15 minutes at 1250 Fahrenheit.

When the ultimate material was tested, it was found to have substantially the same strength and elasticity as standard plain carbon capped steel of 23% carbon content while retaining all of the qualities of rimmed or effervescent steel of necessarily much lower strength and less elasticity, namely, the fine finish and deep-drawing qualities of normal rimmed steel. Furthermore, the central portion or core or the material was free from the metalloid segregation incidental to rimmed or efiervescent steel.

The accompanying drawing illustrates the invention, Figure 1 showing the initial cast 01 rimming steel in an ingot mold, Figure 2 the cast after the formation 01' the frozen skin, and Figure 3, the final cast of diflerent composition which has displaced the still molten rimming steel core and is now in the skin in its place.

In the drawing, I is the ingot mold, 2 is the rimming steel, 3 is the frozen skin of the rimming steel and 4 is the metal of diflerent composition.

I claim:

A method of casting steel, characterized by casting eifervescing steel into an in'got mold, allowing said steel to eilfervesce until a solidified skin forms, casting steel of a different chemical composition into said ingot mold while the central portion of said eilervescing steel is molten to displace said central portion by the second named steel and allowing the latter to solidify and integrally join with said skin, the second named steel being of higher tensile strength than said efiervescing steel by containing a suitable amount of a strengthening element.

JAMES W. KINNEAR, JR. 

